title: A simple quantitative affinity capturing assay of poliovirus antigens and subviral particles by single-domain antibodies using magnetic beads.
abstract: Recently, single-domain recombinant antibody fragments (VHHs or nanobodies) against poliovirus type 1 were isolated. To examine the antigenicity of poliovirus using these recombinant VHHs, an alternative technique mimicking protein A immunoprecipitation had to be developed that was designed specifically for VHHs. The current study validated an affinity capturing assay that is based on the magnetic separation of unbound antigen and antigen-VHH complexes. The technique is simple, fast, reliable, quantitative and inexpensive and was employed to assess the reactivity of 15 VHHs for native infectious poliovirus (N antigen), heat-denatured virus (H antigen) and 14S subviral particles. Three distinct subsets of VHHs were tentatively distinguished based on their specificity for the antigens: one that binds only to 14S precursors, another that binds to the H antigen and a third that binds to the N antigen. Some VHHs of the latter two subsets bound 14S subviral particles with equal affinity but others had at least 100-fold less affinity for the precursors. All neutralizing VHHs were demonstrated to recognize N antigen and all N-specific VHHs were shown to be neutralizing. This study corroborates the findings that VHHs mainly target conformational epitopes and that they target additional epitopes as compared to classical antibodies. The described technique may be useful for epitope mapping and tracking conformational changes of proteins.
authors.affiliation: Department of Pharmaceutical Biotechnology and Molecular Biology, Centre for Pharmaceutical Research, Vrije Universiteit Brussel, Laarbeeklaan 103, B-1090 Brussels, Belgium. bert.thys@vub.ac.be
authors.forename: Bert
authors.initials: B
authors.lastname: Thys
authors.forename: Dirk
authors.initials: D
authors.lastname: Saerens
authors.forename: Lise
authors.initials: L
authors.lastname: Schotte
authors.forename: Gerrit
authors.initials: G
authors.lastname: De Bleeser
authors.forename: Serge
authors.initials: S
authors.lastname: Muyldermans
authors.forename: Gholamreza
authors.initials: G
authors.lastname: Hassanzadeh-Ghassabeh
authors.forename: Bart
authors.initials: B
authors.lastname: Rombaut
mesh_terms: D000914:Antibodies, Viral / Q000276:immunology*; D000936:Antigen-Antibody Complex / Q000302:isolation & purification*; D000956:Antigens, Viral / Q000302:isolation & purification*; D018604:Epitope Mapping / Q000379:methods; D000939:Epitopes / Q000276:immunology; D018189:Immunomagnetic Separation / Q000379:methods*; D017955:Poliovirus / Q000302:isolation & purification*; D011487:Protein Conformation
chemical_list: D000914:Antibodies, Viral; D000936:Antigen-Antibody Complex; D000956:Antigens, Viral; D000939:Epitopes